In recent years there has been a tremendous increase in the use of compact fluorescent lamps in place of conventional incandescent lamps. Because of the longer life and the improved energy efficiency of the compact fluorescent lamp over that of the conventional incandescent lamp, consumers as well as commercial establishments have been willing to convert to the compact fluorescent lamps. An example of such a compact fluorescent lamp can be found in U.S. Pat. No. 4,503,360 issued to D. E. Bedel on Mar. 5, 1985. It will be noted that for the typical compact fluorescent lamp, the lamp envelope is shaped in a manner whereby a plurality of parallel extending tube portions extend from a base portion for a predetermined length.
In order to compare favorably to the incandescent lamps, one area that must be addressed by lamp designers is the ability to achieve higher lumen output levels than are presently achieved; for instance, it would be desirable to provide a compact fluorescent lamp that would achieve substantially the same lumen output as a 75 to 100 watt incandescent lamp. A compact fluorescent lamp of sufficiently high power to give the lumen output of a 100 Watt or higher incandescent lamp while running at currents low enough to be very efficient requires a relatively long arc length of greater than approximately 60 cm. To provide a glass tube with such a length that would fit within the small overall size of the conventional incandescent lamp of the same lumen output, lamp manufacturers have gone to extending the lengths of the respective tube portions of the lamp envelope or, in the alternative, to increasing the number of such tube portions to as many as eight such tube portions. As an example of such an application, some compact fluorescent lamps are produced by bending segments of 12 mm tubing into U-shapes and sealing off one or both legs and then connecting two or more of such bent tubes with glass bridges made by simultaneously blowing out a small hole near the bottom of two tubes and fusing them together. The discharge length then passes up one leg, down the other and then through the glass bridge to the second bent tube arrangement and so forth. Another approach to attaining the longer discharge paths needed for higher wattage lamp configurations is to use a coiled tubular lamp envelope. An example of such an arrangement can be found in German Patent Application No. DE 4133077 filed in Germany on Oct. 2, 1991 and assigned to Narva Berliner Gluhlampenwerk GmbH. In this application, a simple coil arrangement is provided whereby the glass tubing is double wound with an interconnecting bridge portion formed at the top area connecting the two wound coil portions.
Regardless of the configuration of the lamp envelope, whether U-shaped or coiled, there is a need to secure the lamp envelope either to a plug base which can be inserted into an adaptor, or, to a housing arrangement that would also include an integral ballast circuit contained therein. In either instance, it has been found that the adhesive material that is used is dark in color, typically brown, and hence tends to absorb the light output that is generated at the ends of the lamp envelope disposed within the housing or plug member. For a U-shaped lamp envelope where it is possible to have as many as eight such tube ends, there is a significant amount of light lost due to absorption by the adhesive material. One approach to solving this problem of light absorption caused by the adhesive material is to first apply a reflective coating on the ends of the lamp envelope. When such an approach was attempted, it was found that the reflective material could not stay on the ends of the lamp envelope and as such, the adhesive material used to secure the lamp envelope into the base was pulling the reflective coating off of the lamp and therefore resulting in poor adhesion of the envelope to the base.
Of additional concern in mounting the lamp envelope to the housing or plug member, is the fact that UV radiation may escape from the bottom of the lamp envelope ends and be directed down towards the electronic components that make up electronic ballast circuits. It is known that UV over time can deteriorate such electronic components. Accordingly, it would be advantageous if an adhesive material could be developed that would not only reduce the amount of light that is lost through absorption at the lamp envelope ends, but could also be effective in reducing or eliminating the amount of UV radiation that escapes and affects electronic components associated with the ballast circuit.